The invention relates to a twin-pipe shock absorber, of a known type including an oil reservoir between a working cylinder and an outer pipe, a piston which is displaceable in the working cylinder, and one or more bores provided in the piston which form the connection between the spaces above and below the piston.
A non-return upflow valve is provided which can open these bores on the inward stroke of the piston rod for the displacement of oil from the space below the piston to the space above the piston. A hollow piston rod extends towards the top end of the working cylinder. A bottom plate closes the bottom end of the shock absorber, and a disc is fitted between the piston and the bottom plate inside the working cylinder, provided with one or more bores. A non-return upflow valve regulates the upgoing flow through the bores in the disc. A central pipe extends through the piston in the hollow piston rod and also through the disc. A regulated first damper valve is fitted at the bottom end of the working cylinder, and a regulating mechanism is disposed below the first damper valve in order to regulate the flow resistance caused by the above-mentioned first damper valve.
Such a shock absorber is known from international patent application No. PCT/NL 89/00016 in the name of Koni B.V.
The main advantages of this known type of shock absorber are that the shock absorption is essentially independent of the piston speed and that a single regulating mechanism regulates the damping on the ingoing and outgoing stroke. A disadvantage is, however, that the full stroke volume of absorber fluid has to be displaced through the central pipe to the damper valve working in one direction which handles both the damping of the outgoing and of the ingoing stroke. At each stroke a large part of the cylinder contents flows to the reservoir and back. In particular, flowing back in the correct manner limits the maximum achievable piston speed at which the shock absorber still functions in the optimum way, while the dimensions of the piston and the piston rod are also subject to limitations.
The object of the invention is to avoid these disadvantages and to provide a shock absorber of the type mentioned above which still functions well at very high piston speeds, and where no limitations need to be imposed as regards the dimensions of the piston and piston rod.